Glass fiber is an inorganic fiber material that can be used to reinforce resins to produce composite materials with good performance. As a reinforcing base material for advanced composite materials, high-modulus glass fibers were originally used mainly in the aerospace industry or the national defense industry. With the progress of science and technology and the development of economy, high-modulus glass fibers have been widely used in civil and industrial fields such as wind blades, pressure vessels, offshore oil pipes and auto industry.
The original high-modulus glass compositions were based on an MgO—Al2O3—SiO2 system and a typical solution was S-2 glass of American company OC. The modulus of S-2 glass is 89-90 GPa; however, the production of this glass is excessively difficult, as its forming temperature is up to about 1571° C. and its liquidus temperature up to 1470° C. and therefore it is difficult to realize large-scale industrial production. Thus, OC stopped production of S-2 glass fiber and transferred its patent to American company AGY.
Thereafter, OC developed HiPer-tex glass having a modulus of 87-89 GP, which were a trade-off for production scale by sacrificing some of the glass properties. However, as the design solution of HiPer-tex glass was just a simple improvement over that of S-2 glass, the forming temperature and liquidus temperature remained high, which causes difficulty in attenuating glass fiber and consequently in realizing large-scale industrial production. Therefore, OC also stopped production of HiPer-tex glass fiber and transferred its patent to the European company 3B.
French company Saint-Gobain developed R glass that is based on an MgO—CaO—Al2O3—SiO2 system, and its modulus is 86-89 GPa; however, the total contents of SiO2 and Al2O3 remain high in the traditional R glass, and there is no effective solution to improve the crystallization performance, as the ratio of Ca to Mg is inappropriately designed, thus causing difficulty in fiber formation as well as a great risk of crystallization, high surface tension and fining difficulty of molten glass. The forming temperature of the R glass reaches 1410° C. and its liquidus temperature up to 1350° C. All these have caused difficulty in effectively attenuating glass fiber and consequently in realizing large-scale industrial production.
In China, Nanjing Fiberglass Research & Design Institute developed an HS2 glass having a modulus of 84-87 GPa. It primarily contains SiO2, Al2O3 and MgO while also including certain contents of Li2O, B2O3, CeO2 and Fe2O3. Its forming temperature is only 1245° C. and its liquidus temperature is 1320° C. Both temperatures are much lower than those of S glass. However, since its forming temperature is lower than its liquidus temperature, which is unfavorable for the control of glass fiber attenuation, the forming temperature has to be increased and specially-shaped tips have to be used to prevent a glass crystallization phenomenon from occurring in the fiber attenuation process. This causes difficulty in temperature control and also makes it difficult to realize large-scale industrial production.
To sum up, we find that, at present stage, the actual production of various high-modulus glass fibers generally faces the difficulty of large-scale production with refractory-lined furnaces, specifically manifested by comparably high liquidus temperature, high rate of crystallization, high forming temperature, high surface tension, fining difficulty of molten glass and a narrow temperature range (ΔT) for fiber formation and even a negative ΔT. Therefore, most companies tend to reduce the production difficulty by compromising some of the glass properties, thus making it impossible to improve the modulus of the above-mentioned glass fibers with the growth of production scale. The problem of an insufficient modulus has long remained unresolved in the production of S glass fiber.